This invention relates generally to geophones, and in particular to double-ended geophone structures.
Geophones are devices which sense motion by suspending an inertial reference mass structure from a rigid, fixed supporting structure. Typically, the mass is a coil form suspended by springs in a magnetic field, one spring being attached at each end of the coil form. The springs position the coil form within the magnetic field so that the coil form is centered laterally and along its axis within the magnetic field. The springs also form a suspension system having a predetermined resonant frequency.
Geophones may be used in a variety of applications such as, but not limited to, seismic operations on land, in boreholes, in mines, and under water. The operating principle is the same regardless of the application or environment. In seismic operations, seismic waves are imparted into the earth's crust at or near the earth's surface, and portions of those seismic waves are reflected or refracted from the boundaries of subsurface layers. Geophones are generally arranged in arrays or groups on the earth's surface, and when the reflected or refracted waves encounter a geophone, the coil form, which is suspended between the two springs, tends to remain substantially motionless relative to the geophone housing while the geophone housing and its connected magnetic circuit moves with the earth's surface. The movement of the coil form through a magnetic field causes a voltage to be generated at the output of the geophone. The outputs of the arrays of geophones are recorded in a form that permits analysis. Skilled interpreters can discern from the analysis the shape of subsurface formations, and the likelihood of finding an accumulation of minerals, such as oil and gas.
In geophones, both ends of the electrical path have to be electrically insulated from each other and the outside case of the geophone. Typical conventional geophones satisfy this requirement by using insulation sleeves, insulation disks, and other similar devices. Such devices complicate the assembly of the geophone. Furthermore, in typical conventional geophones, both of the signal terminals are positioned on the same side of the geophone. This construction further complicates the assembly.
The present invention is directed to overcoming one or more of the limitations of the existing geophones.